In textile production, synthetic fibres are formed from a “spin-draw” process in which a molten polymer, such as polyester or nylon, is spun into filaments, and twisted together to form a single fibre. The spun fibre is then drawn, altering the fibre's elasticity, tensile strength and diameter. During the process, typically a liquid emulsion or “finish” is applied to the fibre to lubricate the filaments and thereby reduce static electricity generated by the movement of the fibre through processing machinery. Further, interlacing nodes are typically formed in the fibre by exposing the drawn fibre to a pressurized air jet, thereby bonding the individual filaments together at periodic intervals along the fibre.
Lack of uniformity in fibre bulk, finish, denier, or interlacing node distribution can cause fibre entanglement or breakage, or irregularities in fibre coloration during the weaving process, resulting in costly production-line shutdowns for the end-user. Accordingly, attempts have been made to monitor the physical characteristics of fibre in real-time, as it is being produced, to identify defects in the fibre before it is shipped to the end-user.
For instance, Fabbri (U.S. Pat. No. 4,706,014) and Meyer (U.S. Pat. No. 5,394,096) use a capacitive sensor to respectively measure the diameter and denier of a polymer fibre. However, capacitive sensors can only detect large variations in denier. Further, it is not possible to monitor other fibre characteristics of importance to textile users, such as finish, bulk, node count and node quality, using a capacitive sensor.
Sakai (U.S. Pat. No. 4,491,831) uses a phototransistor to detect yarn irregularities. The phototransistor generates an analog signal in response to yarn unevenness. The analog signal is digitized, and then subjected to real-time frequency analysis, to thereby detect both cyclic and non-cyclic yarn irregularities. However, it is not possible to monitor other fibre characteristics of importance to textile users, such as finish, bulk, node count and node quality, using a phototransistor.
Felix (U.S. Pat. No. 4,888,944) monitors a pair of process parameters, such as yarn tension and speed, to detect changes in denier, filament breakage, and absence of finish. However, using the disclosed monitored parameters, it would not be possible to monitor other fibre characteristics of importance to textile users, such as bulk, node count and node quality.
Instrumar Ltd. (CA 2,254,426) uses an electric field sensor for measuring physical fibre characteristics in real-time. Changes in the physical characteristics of a fibre as it is drawn past the sensor causes a current to be induced in the electrode. Comparing the changes in magnitude and phase of the induced current against known fibre profiles allows Instrumar to monitor the denier, finish and interlacing of the drawn fibre in real-time. However, the electrode is sensitive to changes in electric field adjacent to the fibre, thereby reducing the sensitivity of the sensor to the desired fibre characteristics. Further, it is not possible to monitor other fibre characteristics of importance to textile users, such as bulk and node quality, using the described sensor measurements.
Therefore, there remains a need for an improved mechanism for monitoring the physical characteristics of multiple-filament fibre in real-time.